Method for managing the heating of water in a tank of a water heater

ABSTRACT

The invention relates to a method for managing the heating of water in a tank of a water heater which comprises a device for electrically heating the water in the tank, characterized in that it comprises, when a water heating phase is actuated: activation of heating by the heating device, determination of a variation of the temperature in the tank over time and determination of at least one water filling state in the tank according to the variation over time.

FIELD OF THE INVENTION

The present invention relates to water heating appliances also referredto as water heaters. It particularly relates to a method for managingwater heating intended to prevent any shortage of water in the waterheater.

TECHNOLOGICAL BACKGROUND

Water heaters are devices for heating water for various household orindustrial needs. The term water heater denotes a water storageappliance which has at least one tank serving as a hot water storageheating body, also frequently referred to as a boiler. The water isadmitted into the storage tank where it is intended to be heatedtherein. Furthermore, the invention relates to an electric water storagewater heater. The capacity of such a tank is more or less greataccording to the requirements to which storage appliances are assigned,for example by being associated with one or more bathroom sink taps, ashower and/or a bath, etc.

In a known manner, an electric water heater generally has a heatingelement immersed in the tank serving as a heating body for heating thewater contained therein. The water in the tank of a water heater isnaturally stratified if it is not mixed: hot water at the top and coldwater at the bottom.

The temperature of the water in the heating body is, in a known manner,monitored by a sensor or a probe, said probe being immersed in the tankand positioned preferably in the vicinity of the water heating device.The probe cannot be placed too close to the heating device as, in thiscase, the probe would detect the temperature of the heating device andnot the temperature of the water to be heated. The drawback of thisprobe, intended to measure the temperature of the water, is that it isnot configured to sense effectively or above all rapidly overheating ofthe heating device; said device being liable to continue heating untilthe irremediable damage thereof in the event of it being unable toexchange the heat thereof effectively with the water. The problem isparticularly evident for water heaters comprising a heating device inthe form of a resistor. Indeed, resistors are known to have aparticularly small exchange surface area with water, while requiring asignificant time to heat the water. As such, it proves to beparticularly difficult to detect, finely and reactively, overheating ofthe heating device. Overheating is very frequently detected too lategiving rise to irreversible damage for the water heater and the heatingdevice.

As such, overheating of the heating device is a known major problem, dueto a lack of heating body heat exchange, to a lack of irrigation or toexcessive scaling.

The present invention makes it possible to solve all or, at least, someof the drawbacks of current techniques. A problem underlying the presentinvention is that of proposing a method for managing heating preventingoverheating of the heating device by detecting a probable shortage ofwater in the tank of the water heater.

SUMMARY OF THE INVENTION

To achieve this aim, the invention envisages a method for managing theheating of water in a tank of a water heater which comprises a devicefor electrically heating the water in the tank, characterized in that itcomprises, when a water heating phase is actuated: activation of heatingby the heating device, determination of a variation of the temperaturein the tank over time and determination of at least one water fillingstate in the tank according to the variation over time.

The method according to the present invention also envisages,preferably, during the heating phase: periodic determination of avariation of the temperature in the tank over time during a predefinedtime interval, determination of an insufficient water filling state ofthe tank when a positive variation over time greater than a predefinedvalue is detected and shutdown of the heating following thedetermination of the insufficient filling state.

The invention also relates to a system for heating water in a tank of awater heater, comprising a device for electrically heating the water anda device for managing heating configured to actuate the activation anddeactivation of the heating device, characterized in that the device formanaging heating comprises at least one temperature measurement sensorsuitable for measuring a temperature in the tank and means arranged tocarry out the method according to any one of the preceding claims.

The technical effect, induced by the method and the system for heatingwater of a water heater according to the invention, is that ofpreventing the risks of overheating in a water heater by detecting aninsufficient water level in the tank of the water heater, liable tocause malfunctions of the water heater. The invention thus relates to adetection method that is relatively simple to implement and inexpensivesuitable for avoiding, in the event of overheating of the heatingdevice, water heater repair or replacement costs, which prove to berelatively high.

Advantageously, detection of a problem, particularly of insufficientwater filling, takes place after a slight heating of the device suchthat no risk of material damage is involved. Particularlyadvantageously, the method according to the present invention, suitablefor detecting a shortage of water in the tank, is performed at start-upbut also during the heating time. The lack of water in the tank mayarise at any time, it is thus advantageous for the protection to becontinuously active.

BRIEF INTRODUCTION TO THE FIGURES

The aims, subject matter, and features and advantages of the inventionwill emerge more clearly from the detailed description of an embodimentthereof which is illustrated by the accompanying figures wherein:

FIG. 1 illustrates a cross-section of a water heater. The water heatercomprises a tank intended to hold a volume of water and a heatingdevice.

FIG. 2 illustrates a cross-section of the sheath wherein a heatingelement is situated.

FIG. 3 illustrates a cross-section of the inside of the sheath.

FIG. 4 is a view of a supporting member intended to be housed inside thesheath.

FIG. 5 illustrates a schematic representation of the different steps ofthe method according to the invention relative to time and temperaturevariables.

The drawings are given by way of example and are not limiting in respectof the invention. They constitute schematic principle representationsintended to facilitate the comprehension of the invention and are notnecessarily to the scale of the practical applications.

DETAILED DESCRIPTION

Before beginning a detailed review of embodiments of the invention,optional features which may optionally be used in association oralternatively are listed hereinafter:

-   -   Advantageously, the determination of at least one filling state        comprises the determination of an insufficient filling state        when a positive variation over time greater than a predefined        value is detected.    -   Preferentially, continuation or resumption of heating is        inhibited following the determination of the insufficient        filling state.    -   Advantageously, the inhibition is maintained until the        determination of a sufficient filling state.    -   Particularly advantageously, during the inhibition, a second        determination of a temperature variation over time is performed,        a second determination of a water filling state of the tank is        performed, comprising the determination of a sufficient filling        state when a negative variation over time less than a predefined        value is detected.    -   Preferably, the determination of at least one filling state        comprises the determination of a sufficient filling state when a        positive variation over time less than a predefined value is        detected.    -   Preferentially, the heating phase is performed, actuated on        determining the sufficient filling state.    -   Particularly advantageously, the determination of at least one        filling state comprises the determination of a scaling state        when a positive variation over time at least 10% less than the        predefined value (D1) and preferably at least 25% less is        detected.    -   Advantageously, during the heating phase, periodic determination        of a variation of the temperature in the tank over time during a        predefined time interval, determination of an insufficient water        filling state of the tank on determining a positive variation        over time greater than a predefined value, shutdown of the        heating following the determination of the insufficient filling        state are performed.    -   Preferentially, the determination of a variation over time is        performed by calculating the ratio of the difference between a        temperature measured on activating heating and a temperature        after a predefined time, and the predefined time.    -   The predefined time is preferably between 2 and 4 minutes.    -   Preferentially, the heating is performed at a power less than        1500 kW. These values vary according to the characteristics of        the tank, notably the volume thereof.    -   Advantageously, the heating is stopped before the determination        of at least one filling state.    -   Particularly advantageously, a heating device including at least        one inductor and at least one load is used, the inductor being        configured to produce an induced current in the load. This        technique can be transposed to other, particularly resistive,        heating systems. The advantage of the induction system is, on        one hand, the ease of control of the power, and, on the other,        the presence of electronic temperature sensors associated with a        high-performance processing system (microcontroller) for        carrying out with precision heating and temperature measurement        sequences during these heating phases.    -   Preferentially, the heating device includes at least one        inductor and at least one load, the inductor being configured to        produce an induced current in the load.    -   The water heater preferably includes a tank suitable for holding        water and a system according to the invention.    -   Advantageously, the tank is delimited by a peripheral jacket and        the wall of a sheath situated in the internal volume of the        peripheral jacket, the heating device being at least partially        immersed in the sheath.    -   Preferentially, the load is formed at least partially by the        wall of the leak-tight sheath and the inductor is housed in the        sheath.

FIGS. 1 to 4 describe an example of a water heater comprising a devicefor electrically heating water and a device for managing heatingconfigured to actuate the activation, monitoring and deactivation of theheating device, for executing the method according to the invention.

FIG. 1 illustrates a cross-section of a water heater 1. The water heater1 comprises a tank 2 intended to hold a volume of water and a heatingdevice. The tank 2 has, for example, a capacity greater than 10 liters,preferably, greater than 20 liters. The tank 2 is delimited on one handby a peripheral jacket 3 and, on the other, by the wall 4 of aleak-tight sheath 5 immersed in the internal volume of the peripheraljacket 3. The tank comprises an opening 7, preferably in the form of atrap door, for inserting the heating element, this heating element beingsuitable for being inserted into a sheath in turn suitable for beinginserted via the opening 7. The tank 2 comprises at one of thelongitudinal ends thereof two orifices: one inlet orifice 6 a of waterintended to be heated and one heated water outlet orifice 6 b.

The heating device comprises at least one inductor 10 housed in thesheath 5 and at least one load formed by at least one portion of thewall 4 of the sheath 5. The inductor 10 is advantageously, indirectly,heat-generating. The induction heating principle has numerousadvantages. Induction requires a magnetic field generating an inducedcurrent and, thus, heating in this load. The inductor 10 mayadvantageously be positioned on a supporting member 9. Particularlyadvantageously, the supporting member 9 simplifies the winding phase inthat it serves both for the embodiment of the inductor 10 and also forholding same in the water heater 1. This makes it possible to avoid longand costly phases for solidifying the induction coil so as to ensure themechanical cohesion thereof (i.e. for example thermo-adhesion). Thesupporting member 9 is fixedly mounted in the sheath 5. Preferably, thesupporting member 9 is fixed relative to the sheath 5 by only one of theends thereof situated on the side of an opening 7; said opening 7 beingsituated via the peripheral jacket 3 of the water heater 1, at one ofthe longitudinal ends of the water heater 1.

Preferentially, the tank 2 and/or the sheath 5 and/or the inductor 10have cylindrical shapes. According to a further embodiment, the sheath 5and the inductor 10 have rectangular parallelepipedic shapes. In thelatter case, the tank 2 adopts, particularly advantageously, arectangular parallelepipedic shape so as to offer space-saving in use.

The water heater also comprises a device for managing heating at leastone secondary heat sheath 8 intended to monitor the temperature insidethe tank 2. The secondary sheath 8 may be presented in the form of atube. This secondary sheath 8 is preferentially a sheath of smalldiameter suitable for receiving a temperature sensor which is, forexample, an NTC (Negative Temperature Coefficient) type probe, the NTCprobe being a thermistor wherein the resistance decreases uniformly withthe temperature. It is necessary to ensure that the thermal contactbetween the secondary sheath 8 and the temperature probe positionedtherein is correct. The secondary sheath 8 extends along thelongitudinal direction of the sheath 5. The secondary sheath 8 issituated in the vicinity of the outer wall 4 of the sheath 5 and, forexample, at less than 2 centimeters.

FIG. 2 illustrates a cross-section of the sheath 5. The wall 4 of thesheath 5 is leak-tight so as to prevent water from entering the heatingdevice. The wall 4 of the sheath 5 is advantageously formed from a steelsheet of thickness, for example, between 0.4 millimeters (mm) and 2.3millimeters. Advantageously, the sheath 5 is enameled similar to theinside of the tank 2; the enamel adhering best on decarburized steel.Decarburized steel is very magnetic and thus proves to be a good loadfor an induction heating system. It should be noted that the heatingpower is dissipated in a thickness of approximately 0.4 mm (inductionfrequency of 20 kHz) in relation to the induction system and thus thatit is necessary for the thickness of the sheath to be at least athickness of 0.4 mm. The sheath 5 includes an opening for access to oneof the ends thereof, the supporting member 9 being inserted into thesheath 5 via said end.

The secondary sheath 8 is preferentially attached by one of thelongitudinal ends thereof on a first face of a plate 12 before beinginserted into the tank 2. The secondary sheath 8 is a tube welded ontothe same plate 12 as the sheath 5 and is enameled like said sheath 5.The plate 12 herein has the shape of a disk. The plate 12 is attached tothe outer wall of the tank 2 via a seal. Advantageously, the sheath 5comprises a base 11 attached to one of the longitudinal ends thereof.The base 11 is preferably in the shape of a disk or a square.Particularly advantageously, the heating device inside the sheath 5 canbe removed from the water heater by merely removing the attachmentmeans. Exceptionally, the heating device can be inspected, checked, oreven replaced without opening thus without having to drain the tank 2.

The supporting member 9 serves as a supporting member for the coil 22.In order to “coil”, the coil 22 wire 21 is inserted inside thesupporting member 9 and crimped at the end of the base 11. The wire 21is then stretched and passed through a slot of the bearing surface 13situated at one of the ends of the supporting member 9. The supportingmember 9 can then be attached on the winder (similar to a turningmachine) and the coil 22 wire 21 which is inserted via the slot of thebearing surface 13 of the supporting member 9 is then immediatelylocated in the correct position to start winding. At the end of winding,the wire is cut and inserted through securing slots 19 or notches untilthe bearing surface 14 situated at the other end of the supportingmember 9 is reached. Advantageously, the supporting member 9 comprises aplurality of slots 19 as different inductor versions according to thepower requirement are envisaged. The notches or slots 19 serve to lockthe coil 22 wire 21 which is then reinserted in the center of thesupporting member 9 to join the outgoing wire 21, but diametricallyopposite. The two wires 21 are connected to the respective connectorsthereof rigidly connected to the base 11.

FIG. 3 illustrates a cross-section of the inside of the sheath 5 and thesecondary sheath 8. The inductor 10 includes a coil 22 formed on thesupporting member 9. The supporting member 9 includes a lateral outersurface provided with a coil portion 22 and a fixing portion 13. Thecoil portion 22 is set back relative to the fixing portion 13. Thefixing portion comprises a bearing surface 13 on the internal wall ofthe sheath 5. The bearing surface 13 includes two portions situated oneither side of the coil portion 22 along a longitudinal direction of thesheath 5. The offset 17 of the coil portion 22 relative to the fixingportion 13 is greater than the thickness of the coil 22. The space 16separating the coil 22 and the internal face of the wall 4 of the sheath5 is, preferably, less than 5 millimeters and, advantageously, less than1 millimeter. Surprisingly, it is advantageous for the coil 22 of theinductor 10 to be positioned in the vicinity of the sheath 5. Thisfavors a concentration of the heating on only one portion of thethickness of the sheath 5. It should be noted that, surprisingly, aperson skilled in the art tends to separate induction type coils fromthe heated elements. Indeed, as their name suggests, the heated elementsheat and tend to induce the heating of the induction systems if they arepositioned too close. However, the induction coils are generallyinsulated with organic varnishes, the most effective whereof cannotwithstand temperatures greater than 220° C. In the present invention,heating is advantageously applied to the internal wall 4 (of a thicknessfor example of 0.4 mm) of the sleeve 5 which is heated. However, thesheath 5 is immersed in the water with which it exchanges the heatthereof. During the heating phase, the temperature of the sheath 5 isthus always greater than the temperature of the water for heat exchangeto take place, but the difference in temperature remains small, forexample 30° C. for an injected power of 1800 Watts (W). For this reason,if the maximum temperature of the water to be heated is 65° C., thesheath 5 attains a maximum of 95° C. and the sheath 5 can then beconsidered to be a cold zone for the induction coil 22. It is thenadvantageous to move the induction coil 22 closer to the sheath 5 so asto cool same. This moving closer together is also advantageous for thedesign thereof as the coupling with the load is then increased andtherefore the induction system 10 needs less ampere-turns in order tofunction correctly with the associated inverter thereof, which increasesthe yield of the whole and thus lowers the cost. Finally, it should benoted that it may be necessary to insert an additional electricalinsulator around the coil 22 in the event of the distance, between thecoil 22 and earthed sheath 5, becoming small.

The bearing surface 13 and the internal face of the sheath 5 arearranged in a slide fit. Particularly advantageously, during theinsertion of the supporting member 9 into the sheath 5 and in use, thebearing surface 13 prevents the coil from coming into contact with theinternal face of the wall 4 of the sheath 5. Advantageously, thediameter of the bearing surface 13, 14, greater than the diameter of thecoil portion 22, makes it possible, on one hand, to protect the coil 22and, on the other, control the insertion play of the supporting member 9comprising the coil 22 in the sheath 5.

FIG. 4 illustrates a view of the supporting member 9. The supportingmember 9 is preferentially presented in the form of a hollow tube.Particularly advantageously, the supporting member 9 is configured so asto engage with the shape of the internal wall 4 of the sheath 5. A firstlongitudinal end of the supporting member 9 comprises a first fixingportion including a base 11, a bearing surface 13, 14 and at least oneslot 19 for holding the coil 22 wire 21. A second longitudinal end ofthe supporting member 9, opposite the first, comprises a bearing surface13, 14 and at least one slot 19, 20 for holding the coil 22 wire 21. Thebearing surface 13, 14 includes, particularly advantageously, aplurality of apices of slots formed on an annular portion of the fixingportion. Preferentially, the slots help balance the supporting member 9inside the sheath 5. They also limit hyperstatic phenomena duringinsertion. The slots advantageously make it possible to simplify thecoil 22. According to one embodiment where the sheath 5 has arectangular parallelepipedic shape, a Pan Cake type induction coil 22will preferably be used, without having to use a supporting member 9.

Advantageously, the wall of the supporting member 9 is open-worked so asto promote heat transfer within the sheath 5, minimize the weight of thesupporting member 9 and thus the cost thereof. Preferably, thesupporting member 9 is formed from materials resistant to hightemperatures such as plastics (for example, BMC “Bulk Molding Compound”comprising Polyester resin or Vinylester) reinforced with glass fibers.In position, the supporting member 9 extends along the longitudinaldirection of the sheath 5. The supporting member 9 is advantageouslyhollow and the center thereof may allow the passage of the coil 22 wire21.

FIG. 5 illustrates a schematic representation of the various steps ofthe method according to the invention relative to variables in respectof time t and temperature T. The various phases presented are merelyexamples of possible scenarios. Furthermore, the temperature variationsare illustrated as being linear, but merely to simplify therepresentation of the principle of the invention, these variationsoptionally having further curve shapes. The device for managing heatingincludes at least one secondary sheath 8 for measuring temperaturesuitable for measuring a temperature in the tank 2 and means arranged toexecute the method. The secondary sheath 8 is advantageously equippedwith a temperature probe. This probe is preferably inserted to a stopinto the secondary sheath 8. The data measured by the sensor are,advantageously, transmitted to means arranged to execute the methodaccording to the invention. Preferentially, these means include amicroprocessor or a microcontroller and are suitable for retrieving thedata, analyzing same and then transmitting control information, forexample, to stop or continue heating to the heating device of the waterheater. These means may comprise any electronic components such asautomatic control systems, memories, data reception and acquisitioninterfaces, for example of temperature, and control interfaces, andinstructions executable by at least one processor to implement themethod presented herein.

When a water heating phase is actuated, a first step at a time t₀,consists of activation of heating by the heating device, after havingpreviously detected the initial temperature T₀ in the tank 2.Preferably, the heating device comprises an inductor 10.

The heating activation starts, preferably, with a phase wherein theenergy is limited so not to damage the heating element and theenvironment thereof should the tank 2 have a shortage of water, or bevery significantly scaled. Particularly advantageously, if the tank 2 isempty, the activation of heating does not give rise to destructiveoverheating, either of the heating system, of the sheath 5, or the tank2. The duration of the test phase is, for example, 1 minute. Followingthis phase, the device is shut down automatically for the time requiredto study the behavior of the tank 2 in respect of temperature. For aduration of 1 minute, the heating is preferentially carried out at apower less than 1500 kW. The heating device has thus generated heat inthe sheath 5. As such, the behavior will be different according towhether the sheath 5 is immersed in water (tank 2 full) or in air (tank2 empty). The temperature sensor being situated in the secondary sheath8 in the vicinity of the sheath 5, the temperature to be detected by thesensor will depend on the interface between the secondary sheath 8 andthe sheath 5, and will thus determine whether water is present in thetank 2 or not.

After a predefined time t₁, for example of 3 minutes, a variation oftemperature over time in the tank 2 is determined. The term variationover time denotes the derivative over time, i.e. the ratio of thedifference between a temperature measured on activating heating and atemperature after a predefined time, and the predefined time. Thepredefined time is preferentially between 2 and 4 minutes. Nonetheless,shorter times are possible (this is dependent on the injected energy,the mass and geometry of the different elements), up to thedetermination of an instant variation, at the temperature dataacquisition frequency.

Hence, following this determination of temperature variation over timein the tank 2, a determination at the time t₁, of a water filling stateof the tank 2 as a function of the variation over time; the aim being todetermine on the basis of the variation over time, the water fillingstate of the tank 2.

The predefined value D₁ represents a mean temperature variation valuebetween the time t₀ and the time t₁, following a given phase havinggenerated a heat supply. The value D₁ advantageously represents a ratioof a difference in temperature measured between two times, and morespecifically a thermal limit corresponding to the transition from waterto air. If there is no water in the water heater 1, the primary sheath 5heats rapidly and transmits the heat thereof to the very close secondarysheath 8, for example situated 6 mm from the sheath 5. In the scenariowhereby the primary sheath 5 is immersed in the water, the energysupplied is not sufficient to increase the temperature of the watersignificantly and thus the temperature progression is slight.

If the variation over time measured in the tank 2 and detected at thetime t₁ is positive less than the predefined value D₁, then this meansthat the sheath 5 is immersed, not liable to damage the water heater 1.That being said, if water is present, in general, the water heater 1 isfull. The water shortage scenario is observed primarily during theinstallation or restarting of the water heater 1 in second homes, forexample. It should be noted that it is necessary to bleed theinstallation in order to drain a water heater 1. In this case, theheating device may, advantageously, continue heating the water incomplete safety, without any risk of overheating and/or damaging thewater heater 1. The possible damage could apply to the heating elementbut also to the enamel of the sheath 5 and the thermal insulation of thetank 2. In the scenario whereby the heating element is changed, thewater heater would then operate with reduced performances. Oxidation,removal of the enamel and degradation of the thermal insulation of thetank 2 could be observed.

If the variation over time measured in the tank 2 and detected at thetime t₁ is positive greater than the predefined value D₁, correspondingto an excessive temperature rise, then this means that the tank 2contains an insufficient water level, liable to damage the water heater1 significantly. Overheating of the heating device in the tank 2 maygive rise to serious damage such as the malfunction, or the destructionof the water heater 1, liable to incur relatively high replacement orrepair costs.

As such, if the variation over time is positive greater than D₁ then, atthe time t₁, an inhibition of continuation of heating is performed. Thetime interval between t₁ and t₂ corresponds to a waiting time which isnot significant in the light of the time required for heating the waterof the tank 2. After an increase in the temperature associated with thegiven phase at the time t₀, a peak temperature T₁ is observed at thetime t₁ followed progressively by a decrease in the temperaturecorresponding to normal cooling of the sheath 5 following the shutdownof the heating device.

After a time t₂, FIG. 5 shows the scenario whereby the tank 2 is filledwith water. The entry of water, generally cold, into the tank 2, willgive rise to a significant thermal variation on the sheath 5 and on thesecondary sheath 8 comprising a temperature probe. During theinhibition, i.e. in the time interval t₁ and t₂, a second determinationof a variation of temperature over time is performed, followed by asecond determination of a water filling state comprising thedetermination of a sufficient filling state on determining a negativevariation over time less than a predefined value D₂. This value revealsa limit variation reflecting an intake of cold water.

After filling with water, the variation over time, i.e. the derivativeover time, is detected as being negative, corresponding to a decrease inthe temperature inside the tank 2 in the time interval t₂ and t₃.

After a time t₃, when the predefined temperature T₃ has been reached,corresponding to a sufficient water filling state of the tank 2, aheating phase is performed. During the heating phase, a periodicdetermination of a variation of temperature over time in the tank 2during a predefined time interval, for example between t₃ and t₄, iscarried out. If the variation over time measured at this time ispositive less than a predefined value D₃ then the filling state of thetank 2 is deemed to be sufficient, the method for heating water in thetank 2 is continued. This phase is similar to the heating activationphase carried out at the start of the method, from the time t₀.

As of the time t₄, when no anomaly is detected in the heating device,then the power may advantageously be increased to as to heat the waterof the tank 2 more rapidly. It is thus possible, for example, toimplement a heating power in test mode at a low level and one or aplurality of values, which are higher, in effective heating mode, if thetests are conclusive.

The steps for monitoring the variation of temperature over time arerepeated several times, or even periodically and continuously, duringthe heating phase so as to check the sufficiency of the level of thewater present in the tank 2. If during these checks, a positivevariation over time greater than a predefined value is detected, thismeans that the water filling state of the tank 2 is insufficient, theheating device is then shut down.

The method according to the invention thus makes it possible to detectand prevent any overheating problems, very frequently caused by a waterfilling shortage of the heating body 2. This shortage notably includesan empty tank 2 but also a partially filled tank 2, below a predefinedfilling level.

According to one complementary or alternative embodiment to thedetection of a shortage of water in the tank 2, the method according tothe invention may advantageously be suitable for detecting scaling ofthe heating element.

Following the preliminary heating test phase, the heating device is shutdown automatically for the time required to study thetemperature-related behavior of the tank 2, the heating device havinggenerated heat in the sheath 5. Advantageously, the heating time mayvary and have a different duration to that envisaged during the heatingtest phase. As such, the temperature-related behavior will be differentaccording to whether the sheath 5 is immersed in water (tank 2 full), inair (tank 2 empty) or the sheath 5 is scaled.

The temperature sensor advantageously situated in the secondary sheath 8will determine whether water is present in the tank 2 or whether thereis severe scaling of the heating element. In the scenario whereby theheating element is subject to significant scaling, the primary sheath 5will not be heated rapidly. The energy supplied is not sufficient tosignificantly increase the temperature of the water and, for thisreason, the temperature progression is very slight.

If the variation over time measured in the tank 2 and detected at thetime t1 or at another time is positive and very considerably less thanthe predefined value D1, then this means that the sheath 5 is immersedand very possibly scaled.

According to one embodiment, when a very slight temperature variation isdetected, an alert signal may be activated in order to inform the userof any scaling of the heating element. In this case, the user would havethe choice of descaling the device in order to avoid incurringsignificant replacement or repair costs. Advantageously, one alternativewould be to reduce the heating power to protect the heating element andthe environment thereof. Particularly advantageously, these variousactions may be controlled by a microprocessor.

The use of the method according to the invention for induction heatingsystems, particularly those housed in a sheath 5, is advantageous assuch heating may be brief and have readily adapted powers. As such, thetest phases of the invention may be carried out without significantheating energy production and thus without a risk of material damage andat a low electricity consumption.

The present invention is not limited to the embodiments described abovebut extends to any embodiment covered by the claims.

REFERENCES

-   1. Water heater-   2. Tank or heating body-   3. Peripheral jacket-   4. Wall of sheath-   5. Sheath-   6 a, 6 b. Orifice-   7. Opening-   8. Secondary sheath-   9. Supporting member-   10. Inductor-   11. Base-   12. Plate-   13, 14. Bearing surface-   16. Space-   17. Offset-   19. Slot-   21. Wire-   22. Coil-   D₁, D₂, D₃. Predefined values-   t₀, t₁, t₂, t₃, t₄. Time correspond to temperature measurements-   T₀, T₁, T₂, T₃, T₄. Temperatures measured at different times

The invention claimed is:
 1. A method for managing heating of water in atank of a water heater which comprises a heating device for electricallyheating the water in the tank, wherein said method, when a water heatingphase is actuated, comprises the steps of: activating heating by theheating device, the heating being performed at a first level ofelectrical power; determining a variation of a temperature of the waterin the tank over time during a predefined time interval by determining afirst temperature of the water in the tank, waiting a predefined timeand determining a second temperature of the water in the tank, thevariation of the temperature of the water in the tank being a functionof the first temperature of the water in the tank and the secondtemperature of the water in the tank; determining at least one waterfilling state in the tank according to the variation of the temperatureof the water in the tank over time, comprising: determining aninsufficient water filling state of the tank when a positive variationover time greater than a predefined value D3 is detected, or determininga sufficient water filling state when a positive variation over timeless than a predefined value D1 is detected; if the positive variationover time greater than the predefined value D3 is detected, shuttingdown the heating following a determination of the insufficient waterfilling state; and if the positive variation over time less than thepredefined value D1 is detected, performing further heating by theheating device, the further heating being performed at a second level ofelectrical power that is greater than the first level of electricalpower.
 2. The method according to claim 1, wherein the determining theat least one water filling state further comprises determining aninsufficient water filling state when a positive variation over timegreater than the predefined value D1 is detected.
 3. The methodaccording to claim 2, further comprising inhibiting a continuation ofheating following a determination being made in the determining the atleast one water filling state of the insufficient water filling statewhen the positive variation over time greater than the predefined valueD1.
 4. The method according to claim 3, wherein the inhibiting ismaintained until a determination is made in the determining the at leastone water filling state of the sufficient water filling state.
 5. Themethod according to claim 4, wherein, during the inhibiting, a seconddetermination of a temperature variation of the water in the tank overtime is performed, and a second determination of a water filling stateof the tank is performed, the second determination of the water fillingstate of the tank comprising determining a sufficient water fillingstate when a negative variation over time less than a predefined valueD2 is detected.
 6. The method according to claim 1, further comprisingdetermining a scaling state exists when a positive variation over timebelow 10% less than the predefined value D1 is detected.
 7. The methodaccording to claim 1, wherein the determining of the variation of thetemperature of the water in the tank over time is performed bycalculating a ratio of a difference between a temperature measured onactivating heating and a temperature after the predefined time, and thepredefined time.
 8. The method according to claim 7, wherein thepredefined time is between 2 and 4 minutes.
 9. The method according toclaim 1, wherein the first level of electrical power is a power lessthan 1500 kW.
 10. The method according to claim 1, wherein the heatingis stopped before a determination in the determining the at least onewater filling state is made.
 11. The method according to claim 1,wherein the heating device includes at least one inductor and at leastone load, the at least one inductor being configured to produce aninduced current in the at least one load.
 12. A system for heating thewater in the tank of the water heater according to claim 1, said systemcomprising the heating device for electrically heating the water and adevice for managing heating, the device for managing heating configuredto actuate activation and deactivation of the heating device, whereinthe device for managing heating comprises at least one temperaturemeasurement sensor suitable for measuring a temperature of the water inthe tank.
 13. The system according to claim 12, wherein the heatingdevice includes at least one inductor and at least one load, the atleast one inductor being configured to produce an induced current in theat least one load.
 14. The water heater including the system accordingto claim 12 and the tank suitable for holding water.
 15. The waterheater according to claim 14, wherein the tank is delimited by aperipheral jacket and by a wall of a leak-tight sheath situated in aninternal volume of the peripheral jacket, the heating device being atleast partially embedded in the leak-tight sheath.
 16. The water heateraccording to claim 15, wherein the heating device of the system includesat least one inductor and at least one load, the at least one inductorbeing configured to produce an induced current in the at least one load,the at least one load is formed at least partially by the wall of theleak-tight sheath, and wherein the at least one inductor is housed inthe leak-tight sheath.
 17. The method according to claim 2, furthercomprising inhibiting a resumption of heating following a determinationmade in the determining of the insufficient water filling state when thepositive variation over time greater than the predefined value D1 isdetected.
 18. The method according to claim 1, further comprisingdetermining a scaling state exists when a positive variation over timebelow 25% less than the predefined value D1 is detected.
 19. The waterheater according to claim 15, wherein the tank is further delimited by awall of a secondary leak-tight sheath situated in the internal volume ofthe peripheral jacket, the at least one temperature measurement sensorbeing at least partially embedded in the secondary leak-tight sheath.20. The water heater according to claim 19, wherein the tank extendsalong a first longitudinal direction, the leak-tight sheath extendsalong a second longitudinal direction being parallel to the firstlongitudinal direction, and the secondary leak-tight sheath extendsalong a third longitudinal direction being parallel to the secondlongitudinal direction.
 21. A water heater including a tank suitable forholding water and a system for heating water of the tank, said systemcomprising a heating device for electrically heating the water and amanaging device for managing heating configured to actuate activationand deactivation of the heating device, wherein: the tank is delimitedby a peripheral jacket extending along a first longitudinal direction,by a wall of a leak-tight sheath situated in an internal volume of theperipheral jacket and extended along a second longitudinal direction andby a wall of a secondary leak-tight sheath situated in the internalvolume of the peripheral jacket and extended along a third longitudinaldirection, the second longitudinal direction being parallel to the firstlongitudinal direction and the third longitudinal direction beingparallel to the second longitudinal direction; the heating device is atleast partially embedded in the leak-tight sheath and includes at leastone inductor and at least one load, the at least one inductor beingconfigured to produce an induced current in the at least one load, theat least one load being formed at least partially by the wall of theleak-tight sheath; and the managing device comprises at least onetemperature measurement sensor suitable for measuring a temperature inthe tank and is at least partially embedded in the secondary leak-tightsheath.